Electrical switchboards and other forms of electrical enclosures are typically constructed with cubicle or enclosure access doors having openings through which the electrical switching device operating handles extend for convenient manual operation by personnel without the necessity of opening the access doors. As a safety precaution, it is common practice to equip such enclosures with interlocks functioning to prevent or at least discourage opening of the access door unless and until the switching device therein is open, i.e., OFF.
There are occasions however when it would be most advantageous, if not an absolute necessity, from the standpoint of avoiding disruption of electrical service, for maintenance personnal to gain access to the enclosure without first having to open the switching device. As a consequence, these door interlocks should somehow be defeatable. One way of accomplishing this would be to install the interlock in a manner such that it can be completely removed. This is not a particularly attractive recourse in view of the time and effort required of authorized maintenance personnel. Moreover, defeating the door interlock by its complete removal would be a readily apparent recourse to unauthorized personnel bent on access to the enclosure, and thus any facility in doing so would detract from the intended purpose of discouraging unauthorized access while the switching device is closed. Thus, for the interlock to be effective for its intended purpose, defeatability should be unobvious to uninformed personnel, regardless of whether it is convenient or not.
It is accordingly an object of the present invention to provide a door interlock for effectively discouraging access to an electrical enclosure while the switching device therein is closed, and yet is readily defeatable by informed, authorized personnel.
A further object of the present invention is to provide a door interlock of the above character which is equipped with unobtrusive interlock defeating provision.
Yet another object of the present invention is to provide an interlock of the above character having provisions preventing closure of the switching device while the access door is open.
An additional object is to provide a door interlock of the above character which is simple in construction, economical to manufacture, reliable in service, convenient to operate by operating personnel in its undefeated condition and readily defeatable by informed maintenance personnel.
Other objects of the invention will in part be obvious and in part appear hereinafter.